Electrothermal smelting of steel from scrap has been reserved mainly for electric arc furnaces for a long time. Other smelting equipment, such as induction furnaces, find their use in the steel industry limited by the special prerequisites of charge materials, as well as by the limitations on practicable slag metallurgy.
The advantages of electric arc furnaces, such as high smelting capacity due to concentration of great quantities of energy, considerable independence from the physical quality of the scrap (however, the latter having an essential influence on energy consumption), as well as the possibility of a controlled slag metallurgy, are accompanied by disadvantages. They are noise pollution, particularly during the smelting period, strong fluctuations in power requirements, particularly during the smelting periods and consequently great demand on the power lines, and high combustion losses due to the direct effect of the arc on the scrap during the smelting period, and on the steel bath during the refining period. This is accompanied by great iron losses due to evaporation, as well as by the accumulation of large quantities of fumes.
Other disadvantages include increased iron losses due to working with slag of relatively high iron content with relatively high specific slag quantity, increased energy losses due to constant working with an arc, which as an unfavorable thermal efficiency factor resulting from radiation losses, and working with relatively great specific slag quantities so that the kinetically unfavorable border area reactions between the steel bath and the slag take place within a reasonable period of time. Still further disadvantages include absorption of nitrogen from the furnace atmosphere by ionization in the arc, and the consequent influence on the bare steel bath at the focal point of the electrodes, utilization of expensive graphite electrodes, and the limitation of furnace capacity resulting from limited diameter of graphite electrodes. Also, there is great wear on the refractory lining material especially caused by radiation heat from the arc, by the additional mechanical and thermal stresses of the charge and tilt operations, as well as by the additional chemical attack on masonry and particularly the cap by the iron contained in the flue gas, burning in the arc and oxydizing in the furnace atmosphere, and the intense heat, especially due to the charge-type feeding of scrap and, during refining periods, operating with partially opened furnace doors.
It is the subject of the invention, while maintaining the advantages of the electric arc furnace to eliminate the disadvantages noted above with respect to pollution of the environment, to improve the specific consumption and operating data, as well as to obtain optimum thermal and metallurgical performance in the entire process. The invention is directed to a method of smelting steel from scrap in an electric arc furnance wherein the disadvantages are eliminated by having the scrap continuously smelted in a bath constantly covered by a layer of slag, whereby heat is supplied by means of electrodes immersed in the slag layer.